Molecular disorder effects in the thermal conductivity of solid thiophene

The temperature dependence of the thermal conductivity κ(T) of solid thiophene is measured in a sequence of stable orientationally disordered phases with different degrees of orientational ordering of the molecules: in orientational glass (V_g); in phase V with large angular librational molecular vibrations; in incommensurate phase IV with a static orientational disorder; and in orientationally disordered crystalline phase III with dynamic orientational disorder of the molecules. Measurements are made at the saturated vapor pressure in a temperature range of 2–180 K. It is found that the thermal conductivity of thiophene is practically independent of temperature in phases III and V with dynamic orientational disorder of the molecules. In the orientational glass state and in the incommensurate state, the temperature dependence of the thermal conductivity of thiophene has a form typical of crystals with a long-range orientational order. A distinct hysteresis of the thermal conductivity is found at temperatures slightly below the temperature of the transition from phase IV into phase V.